yams #292411 Schema fingerprint [in-progress]

In order to quickly and safely check if two schema (say, the 'schema.py' one and the one in the database) matches, a fingerprint could be used.

A SHA-1 of the serialized schema for example.

CW could then store it in its database, and use it to rebuild test database automatically when needed, or warn the user about a potential schema problem when starting an instance.

done in<not specified>
closed by<not specified>
patch[schema] Add a fingerprint() method [in-progress]